Abstract: A fuel cell (100) includes a membrane electrode assembly (110) located together with a layer of variable porosity porous gas diffusion material (150). The variable porosity gas diffusion material layer (150) operates to selectively limit the amount of reactants reaching localized areas of the membrane electrode assembly (110) in order to reduce hot spots.

Abstract: A passive solar heating system is disclosed which is used in conjunction with doors and windows exposed to solar radiation and having at least partially transparent glazing. Said system comprises a blind having rotatably adjustable slats disposed in a plane substantially parallel to a panel of glazing, a first absorptive screen for converting light energy into thermal energy. Said screen having a plane substantially parallel to that the glazing and a shade or curtain for selectively covering said system having a plane substantially parallel to the plane of the glazing. Adjustment of the blinds, screens and shade permits the desired degree of immergent light to be converted to heat. Alternatively, more than one absorptive screen may be added to increase the efficiency of thermal conversion.